/*
 * Copyright (c) 2011, the Dart project authors.
 * 
 * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.dart.tools.ui.internal.text.html;

import org.eclipse.jface.text.TextPresentation;
import org.eclipse.swt.SWT;
import org.eclipse.swt.custom.StyleRange;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.Reader;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**
 * Reads the text contents from a reader of HTML contents and translates the tags or cut them out.
 * <p>
 * Moved into this package from <code>org.eclipse.jface.internal.text.revisions</code>.
 * </p>
 */
public class HTML2TextReader extends SubstitutionTextReader {

  private static final String EMPTY_STRING = ""; //$NON-NLS-1$
  private static final Map<String, String> fgEntityLookup;
  private static final Set<String> fgTags;

  static {

    fgTags = new HashSet<String>();
    fgTags.add("b"); //$NON-NLS-1$
    fgTags.add("br"); //$NON-NLS-1$
    fgTags.add("br/"); //$NON-NLS-1$
    fgTags.add("div"); //$NON-NLS-1$
    fgTags.add("h1"); //$NON-NLS-1$
    fgTags.add("h2"); //$NON-NLS-1$
    fgTags.add("h3"); //$NON-NLS-1$
    fgTags.add("h4"); //$NON-NLS-1$
    fgTags.add("h5"); //$NON-NLS-1$
    fgTags.add("p"); //$NON-NLS-1$
    fgTags.add("dl"); //$NON-NLS-1$
    fgTags.add("dt"); //$NON-NLS-1$
    fgTags.add("dd"); //$NON-NLS-1$
    fgTags.add("li"); //$NON-NLS-1$
    fgTags.add("ul"); //$NON-NLS-1$
    fgTags.add("pre"); //$NON-NLS-1$
    fgTags.add("head"); //$NON-NLS-1$

    fgEntityLookup = new HashMap<String, String>(7);
    fgEntityLookup.put("lt", "<"); //$NON-NLS-1$ //$NON-NLS-2$
    fgEntityLookup.put("gt", ">"); //$NON-NLS-1$ //$NON-NLS-2$
    fgEntityLookup.put("nbsp", " "); //$NON-NLS-1$ //$NON-NLS-2$
    fgEntityLookup.put("amp", "&"); //$NON-NLS-1$ //$NON-NLS-2$
    fgEntityLookup.put("circ", "^"); //$NON-NLS-1$ //$NON-NLS-2$
    fgEntityLookup.put("tilde", "~"); //$NON-NLS-2$ //$NON-NLS-1$
    fgEntityLookup.put("quot", "\""); //$NON-NLS-1$ //$NON-NLS-2$
  }

  private int fCounter = 0;
  private TextPresentation fTextPresentation;
  private int fBold = 0;
  private int fStartOffset = -1;
  private boolean fInParagraph = false;
  private boolean fIsPreformattedText = false;
  private boolean fIgnore = false;
  private boolean fHeaderDetected = false;

  /**
   * Transforms the HTML text from the reader to formatted text.
   * 
   * @param reader the reader
   * @param presentation If not <code>null</code>, formattings will be applied to the presentation.
   */
  public HTML2TextReader(Reader reader, TextPresentation presentation) {
    super(new PushbackReader(reader));
    fTextPresentation = presentation;
  }

  @Override
  public int read() throws IOException {
    int c = super.read();
    if (c != -1) {
      ++fCounter;
    }
    return c;
  }

  /*
   * @see org.eclipse.jdt.internal.ui.text.SubstitutionTextReader#computeSubstitution (int)
   */
  @Override
  protected String computeSubstitution(int c) throws IOException {

    if (c == '<') {
      return processHTMLTag();
    } else if (fIgnore) {
      return EMPTY_STRING;
    } else if (c == '&') {
      return processEntity();
    } else if (fIsPreformattedText) {
      return processPreformattedText(c);
    }

    return null;
  }

  protected String entity2Text(String symbol) {
    if (symbol.length() > 1 && symbol.charAt(0) == '#') {
      int ch;
      try {
        if (symbol.charAt(1) == 'x') {
          ch = Integer.parseInt(symbol.substring(2), 16);
        } else {
          ch = Integer.parseInt(symbol.substring(1), 10);
        }
        return EMPTY_STRING + (char) ch;
      } catch (NumberFormatException e) {
      }
    } else {
      String str = fgEntityLookup.get(symbol);
      if (str != null) {
        return str;
      }
    }
    return "&" + symbol; // not found //$NON-NLS-1$
  }

  protected void startBold() {
    if (fBold == 0) {
      fStartOffset = fCounter;
    }
    ++fBold;
  }

  protected void startPreformattedText() {
    fIsPreformattedText = true;
    setSkipWhitespace(false);
  }

  protected void stopBold() {
    --fBold;
    if (fBold == 0) {
      if (fTextPresentation != null) {
        fTextPresentation.addStyleRange(new StyleRange(
            fStartOffset,
            fCounter - fStartOffset,
            null,
            null,
            SWT.BOLD));
      }
      fStartOffset = -1;
    }
  }

  protected void stopPreformattedText() {
    fIsPreformattedText = false;
    setSkipWhitespace(true);
  }

  private String html2Text(String html) {

    if (html == null || html.length() == 0) {
      return EMPTY_STRING;
    }

    html = html.toLowerCase();

    String tag = html;
    if ('/' == tag.charAt(0)) {
      tag = tag.substring(1);
    }

    if (!fgTags.contains(tag)) {
      return EMPTY_STRING;
    }

    if ("pre".equals(html)) { //$NON-NLS-1$
      startPreformattedText();
      return EMPTY_STRING;
    }

    if ("/pre".equals(html)) { //$NON-NLS-1$
      stopPreformattedText();
      return EMPTY_STRING;
    }

    if (fIsPreformattedText) {
      return EMPTY_STRING;
    }

    if ("b".equals(html)) { //$NON-NLS-1$
      startBold();
      return EMPTY_STRING;
    }

    if ((html.length() > 1 && html.charAt(0) == 'h' && Character.isDigit(html.charAt(1)))
        || "dt".equals(html)) { //$NON-NLS-1$
      startBold();
      return EMPTY_STRING;
    }

    if ("dl".equals(html)) {
      return LINE_DELIM;
    }

    if ("dd".equals(html)) {
      return "\t"; //$NON-NLS-1$
    }

    if ("li".equals(html)) {
      // FIXME: this hard-coded prefix does not work for RTL languages, see
// https://bugs.eclipse.org/bugs/show_bug.cgi?id=91682
      return LINE_DELIM + HTMLMessages.getString("HTML2TextReader.listItemPrefix"); //$NON-NLS-1$
    }

    if ("/b".equals(html)) { //$NON-NLS-1$
      stopBold();
      return EMPTY_STRING;
    }

    if ("p".equals(html)) { //$NON-NLS-1$
      fInParagraph = true;
      return LINE_DELIM;
    }

    if ("br".equals(html) || "br/".equals(html) || "div".equals(html)) {
      return LINE_DELIM;
    }

    if ("/p".equals(html)) { //$NON-NLS-1$
      boolean inParagraph = fInParagraph;
      fInParagraph = false;
      return inParagraph ? EMPTY_STRING : LINE_DELIM;
    }

    if ((html.startsWith("/h") && html.length() > 2 && Character.isDigit(html.charAt(2))) || "/dt".equals(html)) { //$NON-NLS-1$ //$NON-NLS-2$
      stopBold();
      return LINE_DELIM;
    }

    if ("/dd".equals(html)) {
      return LINE_DELIM;
    }

    if ("head".equals(html) && !fHeaderDetected) { //$NON-NLS-1$
      fHeaderDetected = true;
      fIgnore = true;
      return EMPTY_STRING;
    }

    if ("/head".equals(html) && fHeaderDetected && fIgnore) { //$NON-NLS-1$
      fIgnore = false;
      return EMPTY_STRING;
    }

    return EMPTY_STRING;
  }

  /*
   * A '&' has been read. Process a entity
   */
  private String processEntity() throws IOException {
    StringBuffer buf = new StringBuffer();
    int ch = nextChar();
    while (Character.isLetterOrDigit((char) ch) || ch == '#') {
      buf.append((char) ch);
      ch = nextChar();
    }

    if (ch == ';') {
      return entity2Text(buf.toString());
    }

    buf.insert(0, '&');
    if (ch != -1) {
      buf.append((char) ch);
    }
    return buf.toString();
  }

  /*
   * A '<' has been read. Process a html tag
   */
  private String processHTMLTag() throws IOException {

    StringBuffer buf = new StringBuffer();
    int ch;
    do {

      ch = nextChar();

      while (ch != -1 && ch != '>') {
        buf.append(Character.toLowerCase((char) ch));
        ch = nextChar();
        if (ch == '"') {
          buf.append(Character.toLowerCase((char) ch));
          ch = nextChar();
          while (ch != -1 && ch != '"') {
            buf.append(Character.toLowerCase((char) ch));
            ch = nextChar();
          }
        }
        if (ch == '<') {
          unread(ch);
          return '<' + buf.toString();
        }
      }

      if (ch == -1) {
        return null;
      }

      int tagLen = buf.length();
      // needs special treatment for comments
      if ((tagLen >= 3 && "!--".equals(buf.substring(0, 3))) //$NON-NLS-1$
          && !(tagLen >= 5 && "--".equals(buf.substring(tagLen - 2)))) { //$NON-NLS-1$
        // unfinished comment
        buf.append(ch);
      } else {
        break;
      }
    } while (true);

    return html2Text(buf.toString());
  }

  private String processPreformattedText(int c) {
    if (c == '\r' || c == '\n') {
      fCounter++;
    }
    return null;
  }

  private void unread(int ch) throws IOException {
    ((PushbackReader) getReader()).unread(ch);
  }
}
